Objective: To investigate the impact of the uterine corpus inclination on pregnancy outcomes in in vitro fertilization and embryo transfer (IVF-ET). Design: Retrospective cohort study. Setting: University-based reproductive medicine center. Population: 526 patients underwent their first frozen embryo transfer (FET) cycle. Methods: All patients underwent transvaginal ultrasound examination to measure the distance from the midline of uterine cavity to the ultrasound probe, which indirectly reflect the uterine corpus inclination. The uterine corpus tends toward the horizontal position as the average distance increases. Multivariable regression analysis was used to study the effect of the uterine corpus inclination on pregnancy outcomes, even in different embryo stage cohorts as subgroup analysis. Main outcomes measures: Clinical pregnancy rate (CPR), spontaneous abortion rate, and live birth rate (LBR). Results:The patients were grouped according to the quartiles of the average distance distribution (Group 1, ≤ 1.98 cm; Group 2, 1.99-2.19 cm; Group 3, 2.20-2.50 cm; Group 4, ≥ 2.51 cm). There were statistically significant differences in the CPR and LBR between Groups 1 and 4 in the cleavage-stage ET cohort (CPR: adjusted odds ratio [OR] 0.225, 95% confidence interval [CI] 0.068-0.774; LBR: adjusted OR 0.315, 95% CI 0.100-0.996) (P < 0.05). There were no significant differences among the four groups in pregnancy outcomes in the blastocyst transfer cohort (P > 0.05). The cut-off value of 2.146 cm was calculated to predict the pregnancy outcomes in the cleavage-stage ET cohort. Conclusion:The uterine corpus inclination might be an independent risk factor for the success of cleavage-stage ET